Several studies in recent years have highlighted the potential of Newcastle disease virus (NDV) to be used as a vaccine vector for avian diseases (Krishnamurthy et al., Virology 278, 168-182, 2000; Huang et al., J. Gen. Virol. 82, 1729-1736, 2001; Nakaya et al., J. Virol. 75, 11868-11873, 2001; Park et al. PNAS 103, 8203-8208, 2006; Veits et al PNAS 103, 8197-8202, 2006; Ge et al. J. Virol. 81, 150-158, 2007; Romer-Oberdörfer et al. Vaccine 26, 2307-2313, 2008).
NDV belongs to the Paramyxovirinae family and the Avulavirus genus. NDV replicates in respiratory and gastrointestinal tracts, in the oviduct, and for some isolates, in the nerve system. The transmission is aerogenic and by oral and fecal routes. NDV causes a highly contagious and fatal disease affecting all species of birds, and can infect some mammalian species. The disease can vary from clinically unapparent to highly virulent forms, depending on the virus strain and the host species. The continuous spectrum of virulence displayed by NDV strains enabled the grouping of them into three different pathotypes: lentogenic, mesogenic, and velogenic (Alexander, D. J., Diseases of Poultry, Iowa State Uni. Press, Ames Iowa, 541-569, 1997). Lentogenic strains do not usually cause disease in adult chickens and are widely used as live vaccines in poultry industries in the United States and other countries. Viruses of intermediate virulence are termed mesogenic, while viruses that cause high mortality are termed velogenic. The disease has a worldwide distribution and remains a constant major threat to commercial poultry production.
The NDV genome is a non-segmented negative strand of RNA of approximately 15 kb. The genomic RNA contains six genes that encode the following proteins in the order of: the nucleocapsid protein (NP), phosphoprotein (P), matrix protein (M), fusion protein (F), haemagglutinin-neuramimidase (FIN) and large polymerase protein (L). Two additional proteins, V and W, of unknown function are produced by RNA editing during P gene transcription (Steward et al., 1993, Journal of General Virology 74:2539-2547).
The development of methods to recover non-segmented negative RNA viruses entirely from cloned cDNA, established in recent years, opened up the possibility of genetically manipulating this virus group, including NDV (Conzelmann, K. K., Ann. Rev. Genet. 32, 123-162, 1998; Roberts and Rose, Virology 247, 1-6, 1998). This unique molecular genetic methodology, termed “reverse genetics,” provides a means not only to investigate the functions of various virus-encoded genes (Palese et al., PNAS 93, 11354-11358, 1996; Nagai, Y., Rev. Med. Virol. 9, 83-99, 1999) but also to allow the use of these viruses to express heterologous genes (Bukreyev et al., J. Virol. 70, 6634-6641, 1996; Mebatsion et al., PNAS 93, 7310-7314, 1996; Schnell et al., PNAS 93, 11359-11365, 1996; Hasan et al., J. Gen. Virol. 78, 2813-2820, 1997; He et al., Virology 237, 249-260, 1997; Sakai et al., FEBS Lett. 45, 221-226, 1999). This provides a new method of generating improved vaccines and vaccine vectors.
The recovery systems from cloned cDNA, based on a lentogenic vaccine strain (LaSota) of NDV, were reported simultaneously by two independent groups in 1999 (Peeters et al., 1999; Romer-Oberdorfer et al., 1999). In the first reported system, the full-length NDV cDNA from LaSota strain (ATCC-VR699) was assembled in pOLTV5 transcription vector containing a T7 DNA-dependent-RNA polymerase promoter. Individual clones of the NDV transcriptase complex (NP, P, and L) were cloned in a eukaryotic expression vector. The cotransfection protocol generated several infective centers in infected monolayers (Peeters et al., J. Virol. 73, 5001-5009, 1999). The second system reported for recovery of a lentogenic NDV from cloned cDNA essentially used the same strategy of assembling the full-length antigenomic expression plasmid and support plasmids (Romer-Oberdorfer et al., Journal of General Virology, 80, 2987-2995, 1999). Other systems were developed recently to recover a lentogenic Hitchner B1 (Nakaya et al., 2001) or LaSota strain of NDV (Huang et al., 2001). The only system available for the recovery of recombinant mesogenic NDV was described by Krishnamurthy et al. (2000). This system utilized the vaccinia virus recombinant (MVA) and HEP-2 cells for transfection. The full length clone of the mesogenic strain Beaudette C and the support plasmids (N, P, and L) from the same strain were used for transfection. An additional transcriptional unit encoding the CAT reporter gene was placed between the HN and L genes. The growth of the rNDV expressing the CAT gene was delayed and the virus was attenuated. The CAT reporter gene was stably expressed for several passages in cell culture.
Avian influenza (AIV), sometimes called avian flu, and commonly recognized as bird flu refers to influenza caused by influenza viruses adapted to birds. AIV is a segmented, single-strand, negative sense RNA virus belonging to the family of Orthomyxoviridae, and is classified as a type A influenza virus. Type A virus is the most frequent cause of animal and human influenza. This type occurs in numerous strains or subtypes that are differentiated mainly on the basis of two surface lipid-enveloped membrane proteins, hemagglutinin (HA) and neuraminidase (NA). HA, facilitates entry of the virus into host cells, and NA assists in the release of progeny virus from infected cells (de Jong et al., J Clin Virol. 35(1):2-13, 2006). Influenza type A viruses are divided into subtypes based on their specific HA and NA content. There are 16 different HA subtypes, and 9 different NA subtypes. Many different combinations of HA and NA proteins are possible. Subtypes of influenza A virus are named according to their HA and NA surface proteins. For example, an “H7N2 virus” designates an influenza A subtype that has an HA protein of the H7 subtype and an NA protein from the N2 subtype. Similarly an “H5N1” virus has an HA of the H5 subtype and an NA from the N1 subtype. The H5N1 subtype has specifically been associated with recent outbreaks in Asia, Russia, the Middle East, Europe and Africa (Olsen et al., Science 21; 312(5772):384-8, 2006).
Influenza A viruses can infect humans, pigs, horses, seals, whales, poultry, cats, dogs, ferrets and other animals, but wild birds are their natural host. Aquatic birds constitute the main influenza reservoir from which virus lineages evolved and adapted to their host, e.g., human, swine and equine influenza. Host specificity is not absolute and cross-species transmission may occur as illustrated by the ability of highly pathogenic avian influenza (HPAI) H5N1 subtype to infect human, feline, canine and porcine species.
The highly pathogenic Influenza A virus subtype H5N1 virus is an emerging avian influenza virus of global concern as a potential pandemic threat. H5N1 has killed millions of poultry in a growing number of countries throughout Asia, Europe and Africa. Unlike type B influenza, type A influenza undergoes antigenic shift (at least two different strains of virus combine to form a new subtype) and epidemiologists, infectious disease investigators, and other health experts are acutely concerned that the co-existence of human flu viruses and avian flu viruses (especially H5N1) may provide an opportunity for genetic material to be exchanged between species-specific viruses, possibly creating a new virulent influenza strain that is easily transmissible and lethal to humans (Food Safety Research Information Office. “A Focus on Avian Influenza”. Created May 2006, Updated November 2007).
Since the first H5N1 outbreak occurred in 1997, there has been an increasing number of HPAI H5N1 bird-to-human transmissions leading to clinically severe and fatal human infections. However, because there is a significant species barrier that exists between birds and humans, the virus does not easily cross over to humans. Although millions of birds have become infected with the virus since its discovery, only about 200 humans have died from Avian Flu in Indonesia, Laos, Vietnam, Romania, China, Turkey and Russia combined.
Considering the susceptibility of animals, including humans, to AIV, a means of preventing AIV infection and protecting animals is essential. Accordingly, there is a need for an effective vaccine against influenza.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.